Date of Thesis

5-10-2017

Thesis Type

Masters Thesis

Degree Type

Master of Science in Mechanical Engineering

Department

Mechanical Engineering

First Advisor

Craig Beal

Abstract

While effective in improving handling and passenger safety, current vehicle control systems are generally limited to braking or steering control. This project presents an approach which integrates steering and braking actuation to further improve vehicle stability in critical cornering scenarios. A 3D phase portrait visualization tool enables examination of lateral velocity, longitudinal velocity, and yaw rate. This tool is used to determine vehicle stability under different operating conditions to inform the design of a controller. The proposed hierarchical controller defines a path-following function for the desired cornering radius and determines appropriate braking and steering inputs, using sliding surface control, to drive the vehicle to the desired path. A low-complexity vehicle model is used to formulate the sliding surface, while a high-fidelity model is used to determine optimal inputs. Simulations show that the sliding surface controller design is more effective than a baseline steering controller in keeping the vehicle on the roadway. Examination reveals that the complex sequence of braking and steering inputs is only feasible with the addition of a modern vehicle control system. While average drivers lack the ability to effectively employ such complex sequencing, modern control systems are capable of this coordination. When entering corners at speeds within the capability of the vehicle, but beyond the ability of the driver, these control sequences can help maintain stability to avoid an accident.

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